JEE ADVANCED CHEMISTRY QUESTION SEPTEMBER 2020
Answers
The 1st , 2nd and the 3rd ionization enthalpies I₁ , I₂ and I₃ of four atoms with atomic numbers n, n + 1 , n + 2 and n + 3, where n < 10 are tabulated below. what is the value of n ?
solution : we know, if difference of two successive Ionisation enthalpies is greater than first Ionisation enthalpy (I mean 1st Ionisation between them ) then Valency of element will be number of first Ionisation enthalpy.
for instance, if (I₃ - I₂) > I₂, it means valency of element is 2.
by observing the values of I₁, I₂ and I₃ for atomic number (n + 2) , it is observed that (I₂ - I₁) > I₁ so Valency of element is 1. so the atomic number (n + 2) should be an alkali metal.
also we observe, for atomic number (n + 3) , (I₃ - I₂) > I₂ so, this indicates valency of atomic number (n + 3) is 2. it will be an alkaline earth metal which suggests (n + 1) should be a noble gas and atomic number n should belongs to halogen family. since n < 10, hence n = 9 ( Fluorine )
Therefore the value of n is 9.